The present invention concerns dyestuff-containing pearlescent pigments based on mica flakes coated with metal oxides wherein the dyestuffs are colored aluminum lakes.
Pearlescent pigments of this kind are used in a large variety of fields, for example in cosmetics or as additives to synthetic resins, lacquers and dyestuffs. They are known, for example, from published Federal Republic of Germany patent specification No. 2,429,762 equivalent to U.S. Pat. No. 4,084,983. For the production of its pigments, an aluminum hydroxide layer is first applied to mica flakes coated with metal oxides by the precipitation from an aluminum salt solution. Then, by reaction of the so-coated pigments with hydroxy-containing compounds, water-insoluble colored aluminum lakes are formed as firmly adhering colored materials. These are formed either directly or with the intermediate formation of a sparingly soluble aluminum chelate and a subsequent reaction thereof with a diazotized amine.
These pearlescent pigments can also be produced in a manner analogous to that described in Federal Republic of Germany patent specification No. 1,192,353 in which precipitation of the aluminum hydroxide layer and reaction with a hydroxy-containing compound take place simultaneously so that either the colored lake or the aluminum chelate to be reacted to give the colored lake is fixed directly on to mica flakes coated with metal oxides.
For practically all fields of use of such pigments, their light fastness plays a very important part. In order to improve on their present usefulness and in order posssibly to widen their fields of use, the problem exists of making available colored pearlescent pigments with improved light fastness.